If you go to the U.S. Dept. of Veterans Affairs web site you will find the National Cemetery Administration page. They have a list of headstone and marker inscription abbreviations. This is for branch of service, war service and awards.
Abbrev for ranks for Air Force, Army, Army Air Corps/Forces, Coast Guard, Marine Corps, Merchant Marines, Navy and all others. They also have a nationwide veteran’s grave site locator which is updated daily